Charged particle beam apparatuses have many functions, in a plurality of industrial fields, including, but not limited to, critical dimensioning of semiconductor devices during manufacturing, defect review of semiconductor devices during manufacturing, inspection of semiconductor devices during manufacturing, exposure systems for lithography, detecting devices and testing systems. Thus, there is a high demand for structuring, testing and inspecting specimens within the micrometer and nanometer scale.
Micrometer and nanometer scale process control, inspection or structuring is often done with charged particle beams, e.g. electron beams, which are generated and focused in charged particle beam devices, such as electron microscopes or electron beam pattern generators. Charged particle beams offer superior spatial resolution compared to, e.g. photon beams due to their short wavelengths.
Particularly for electron beam inspection (EBI) technology throughput is of foremost interest. Thereby, it is inter alia referred to, in particular, to surface inspection at low landing energies <500 e V and low secondary electron (SE) extraction fields. Normally, for high current density electron probe generation compound objective lenses are used (superimposed magnetic and electrostatic retarding field lenses). In those lenses the electron energy inside the column is reduced to the final landing energy. Overall performance is determined by the immersion factor which is the ratio of the column energy to the landing energy. The higher the immersion energy the better the performance is. For low landing energies and low SE-extraction fields, the focal power of the objective lens tends to be more and more performed by the electrostatic retarding field lens. Accordingly, the magnetic lens contribution is drastically reduced and, thereby, the overall objective lens performance is lowered causing higher aberrations.
With increasing immersion factor also the focal plane moves upwards into the direction of the source and finally into the lens body. In this case focusing on large samples becomes impossible.
To overcome this problem for low landing energy in combination with low extraction fields, longer focal length electrostatic lenses can be used. This is achieved by increasing the distance between the two electrostatic lens electrodes, which form the retarding lens, i.e. between which the primary beam is decelerated. However, longer focal length lenses have again larger aberrations. For such a solution even the column energy has to be or should be reduced additionally to some extent, which reduces optics performance even more (smaller immersion factor).
In view of the above, it is an object of the invention to provide an improved objective lens and an improved electron beam device that overcome at least some of the problems in the art.